Optical technology is a vital part of modern telecommunications systems. The optical technology toolset includes lightwave sources, such as lasers. A laser typically requires a gain media and appropriate electromagnetic cavity to operate. A simple laser includes two partially reflective mirrors. Partially reflective mirrors reflect some light, but allow some light through as well. One of the mirrors of a laser cavity could be completely reflective. Together, the gain media and mirrors form what is known as a laser cavity. The laser cavity is designed to have an optical loss lower than the optical gain of the gain media as well as appropriate spectral response to encourage oscillation at a desired wavelength.
Techniques for tuning lasers to adjust the wavelength have been developed. The techniques include using diffraction gratings and in-line filters. A diffraction grating is mechanically adjusted to selectively reflect light of a given wavelength band in the laser cavity. Diffraction gratings provide a broad tuning range without introducing excessive amounts of back-reflected light that is outside of the desired wavelength band. Back-reflected light is undesirable because stray reflections can interfere with the desired feedback obtained from filtered light. One drawback to the use of diffraction gratings in external cavity lasers is that diffraction gratings are relatively bulky. On the other hand, in-line filters, such as in-line Fabry-Perot filters, are compact structures although they typically cause excessive amounts of back-reflected light within a laser cavity.